Lithium-ion batteries have the advantages of high voltage, high energy density, no memory effect and environmental friendliness, etc., and have been widely used in portable electronic devices. The earliest positive electrode material used for commercial lithium-ion batteries was LiCoO2. However, LiCoO2 electrode material has disadvantages because of a scarcity, high cost, and high environmental pollution of the Co natural resources. Further, the actual specific capacity of LiCoO2 is lower, because overcharge leads to irreversible capacity loss and an increase in polarization voltage. With intensive researches on the inexpensive and excellent positive electrode materials, a positive electrode material for lithium-ion batteries which can replace the LiCoO2 was discovered. The properties of LiNiO2 are similar to that of LiCoO2.Both of LiNiO2 and LiCoO2 belong to an R-3m space group and have α-NaFeO2 type layered structure. The price of nickel is lower than that of cobalt, the resources of nickel are more abundant than that of cobalt, and the actual specific capacity is high, and the nickel belongs to environment-friendly positive electrode material. However, LiNiO2 has a poor thermal stability, and is prone to phase change during charge and discharge. Further, Ni2+ the position of 3a of Li+, which leads to cationic mixing, so that the electrochemical performance of the material declines sharply. Lithium manganate is an inexpensive positive electrode material with excellent safety and environmental performance, but the material has deficiencies of low specific capacity and energy density, and poor cycling performance at a high temperature. Therefore, a ternary material combining the performances of lithium cobaltate, lithium nickelate and lithium manganate was made. The nickel-cobalt-manganese ternary material can be regarded as the eutectic of lithium nickelate, lithium cobaltate and lithium manganate. Due to the co-doping of Co and Mn, Ni3+ at the position of 3b in LiNiO2 is replaced with Co and Mn to stabilize the layered structure, so that the electrochemical performance of the ternary material can be improved to a certain extent.
Because of the pursuit of high-energy-density power batteries for electric vehicles, the traditional nickel-cobalt-manganese ternary positive electrode material, such as NCM111 type and NCM523 type, cannot meet the requirements, and thus a lithium nickel-cobalt-manganate(LiNi0.6Co0.2Mn0.2O2) ternary material (referred to as NCM622) of higher capacity and energy density was made. However, although the process of the lithium nickel-cobalt-manganate (LiNi0.6Co0.2Mn0.2O2) synthesized by a traditional solid phase method is simple, the particle size distribution of the product is nonuniform, so it is difficult to prepare a target product with a certain stoichiometric ratio, and the electrochemical performance of the product is poor. The co-precipitation method is a common method to synthesize the lithium nickel-cobalt-manganate in laboratories and the industry, and can be used to prepare the lithium nickel-cobalt-manganate (LiNi0.6Co0.2Mn0.2O2) material. The method has the advantages of a simple process, precise control of the experimental parameters, lower sintering temperature, moderate sintering time, and better particle dispersion. But the material prepared by the method fails to show a good electrochemical performance under high voltage of 4.5V. Due to increase in the charging voltage, the specific capacity and energy density of the material will be significantly increased or even multiplied, which is significantly important for the development of high energy density power batteries.
Although the cycling stability of the conventional lithium nickel-cobalt-manganate (LiNi0.6Co0.2Mn0.2O2) has been improved compared with LiNiO2, it is not competitive in capacity and cycle stability compared with LiCoO2 in the prior art.